U.S. patent application number 12/542065 was filed with the patent office on 2010-03-04 for bearing structure, motor, and fan apparatus.
This patent application is currently assigned to Nidec Corporation. Invention is credited to Kiyoto IDA, Koji MURAOKA, Hiroyoshi TESHIMA.
Application Number | 20100054965 12/542065 |
Document ID | / |
Family ID | 41725736 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100054965 |
Kind Code |
A1 |
TESHIMA; Hiroyoshi ; et
al. |
March 4, 2010 |
BEARING STRUCTURE, MOTOR, AND FAN APPARATUS
Abstract
A sleeve support portion is arranged to support a sleeve having
a rotating shaft inserted therein such that the rotating shaft is
rotatable. A plurality of ribs extending in an axial direction is
provided on an inner surface of the sleeve support portion. The
ribs are preferably spaced from each other in a circumferential
direction centered on the rotating shaft, and arranged to make
contact with at least a portion of the sleeve. The ribs include a
plurality of types of ribs, each type of the ribs having a
different axial position of an axial edge, on an axially opening
portion side, of a contact surface thereof which is arranged to
make contact with the sleeve.
Inventors: |
TESHIMA; Hiroyoshi; (Kyoto,
JP) ; MURAOKA; Koji; (Kyoto, JP) ; IDA;
Kiyoto; (Kyoto, JP) |
Correspondence
Address: |
NIDEC CORPORATION;c/o KEATING & BENNETT, LLP
1800 Alexander Bell Drive, SUITE 200
Reston
VA
20191
US
|
Assignee: |
Nidec Corporation
Kyoto
JP
|
Family ID: |
41725736 |
Appl. No.: |
12/542065 |
Filed: |
August 17, 2009 |
Current U.S.
Class: |
417/354 ; 310/90;
384/441 |
Current CPC
Class: |
F16C 2360/46 20130101;
F04D 29/057 20130101; F16C 33/103 20130101; F16C 35/02 20130101;
H02K 5/1675 20130101; F04D 25/062 20130101 |
Class at
Publication: |
417/354 ;
384/441; 310/90 |
International
Class: |
F04D 25/08 20060101
F04D025/08; F16C 35/02 20060101 F16C035/02; H02K 5/167 20060101
H02K005/167 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2008 |
JP |
2008-222466 |
Jul 9, 2009 |
JP |
2009-162471 |
Claims
1. A bearing structure comprising: a rotating shaft; a sleeve
having the rotating shaft inserted therein such that the rotating
shaft is rotatable with respect to the sleeve; a sleeve support
portion having a bottom, being substantially tubular, extending in
an axial direction, and arranged to support the sleeve; and a base
portion connected to an axial end of the sleeve support portion;
wherein the sleeve support portion includes: an opening portion
arranged to receive the rotating shaft; a cavity portion arranged
to contain the sleeve; and a plurality of ribs provided on an inner
surface of the cavity portion and extending in the axial direction,
the ribs being spaced from each other in a circumferential
direction centered on the rotating shaft; wherein each of the ribs
includes a contact surface arranged to contact at least a portion
of an outer surface of the sleeve; and the ribs include a plurality
of different types of ribs, each of the plurality of different
types of ribs having differently positioned axial contact surfaces
on an axially opening portion side thereof.
2. The bearing structure according to claim 1, wherein the
plurality of different types of ribs include at least one
greater-length rib and at least one shorter-length rib; and the
axial contact surface of the greater-length rib is higher on the
axially opening portion side than the axial contact surface of the
shorter-length rib.
3. The bearing structure according to claim 2, wherein the at least
one greater-length rib and the at least one shorter-length rib have
a substantially equal width in a circumferential direction.
4. The bearing structure according to claim 2, wherein the at least
one greater-length rib and the at least one shorter-length rib have
a different width in a circumferential direction.
5. The bearing structure according to claim 2, wherein the at least
one greater-length rib and the at least one shorter-length rib are
arranged such that a radial distance from a shaft center of the
rotating shaft to the axial contact surfaces of the at least one
greater-length rib and the at least one shorter-length rib is
substantially the same.
6. The bearing structure according to claim 2, wherein the at least
one greater-length rib and the at least one shorter-length rib are
arranged such that a radial distance from a shaft center of the
rotating shaft to the axial contact surfaces of the at least one
greater-length rib and the at least one shorter-length rib is
different.
7. The bearing structure according to claim 1, wherein an axial
position of a center of gravity of a rotating body including the
rotating shaft either substantially coincides with, or is located
more on an axially cavity portion side than, an axial position on
the axially opening portion side of an axial end of one of the
plurality of ribs having an axial end located on the axially
opening portion side that is predominantly on the axially opening
portion side of all the plurality of ribs.
8. The bearing structure according to claim 1, wherein the sleeve
includes two axial ends, and both of the axial ends of the sleeve
are positioned within the cavity portion of the sleeve support
portion.
9. A motor comprising: the bearing structure of claim 1; a rotating
motor component arranged to rotate on the rotating shaft together
with the rotating shaft; and a stationary motor component arranged
to be fixed at a given position; wherein the rotating and
stationary motor components are arranged to cause the rotating
motor component to rotate together with the rotating shaft because
of torque produced therebetween due to electromagnetic
interaction.
10. A fan apparatus comprising: the motor of claim 9; and an
impeller arranged to rotate together with the rotating shaft.
11. A bearing structure comprising: a rotating shaft; a sleeve
having the rotating shaft inserted therein such that the rotating
shaft is rotatable with respect to the sleeve; a sleeve support
portion having a bottom, being substantially tubular, extending in
an axial direction, and arranged to support the sleeve; and a base
portion connected to an axial end of the sleeve support portion;
wherein the sleeve support portion includes: an opening portion
arranged to receive the rotating shaft; a cavity portion arranged
to contain the sleeve; and a plurality of ribs provided on an inner
surface of the cavity portion and extending in the axial direction,
the ribs being spaced from each other in a circumferential
direction centered on the rotating shaft, and arranged to make
contact with at least a portion of the sleeve; wherein each of the
ribs includes an opposed surface raised toward an outer surface of
the sleeve relative to the inner surface of the cavity portion, and
opposed to the outer surface of the sleeve; and at least one of the
ribs is a varied rib having a radial distance between the opposed
surface and a shaft center of the rotating shaft that varies with
respect to the axial direction in at least a partial section of an
entire length thereof along the axial direction.
12. The bearing structure according to claim 11, wherein the varied
projection dimension rib has a portion where the radial distance
between the opposed surface and the shaft center gradually
increases toward the axially opening portion side at an axial end
portion thereof on an axially opening portion side.
13. The bearing structure according to claim 11, wherein the
plurality of ribs include: the varied rib; and at least one uniform
rib having a uniform radial distance between the opposed surface
and the shaft center of the rotating shaft with respect to the
axial direction.
14. The bearing structure according to claim 11, wherein an axial
position of a center of gravity of a rotating body including the
rotating shaft either substantially coincides with, or is located
more on an axially cavity portion side than, an axial position on
the axially opening portion side of an axial end of one of the
plurality of ribs having an axial end located on the axially
opening portion side that is predominantly on the axially opening
portion side of all the plurality of ribs.
15. A bearing structure comprising: a rotating shaft; a sleeve
having the rotating shaft inserted therein such that the rotating
shaft is rotatable with respect to the sleeve; a sleeve support
portion having a bottom, being substantially tubular, extending in
an axial direction, and arranged to support the sleeve; and a base
portion connected to an axial end of the sleeve support portion;
wherein the sleeve support portion includes: an opening portion
arranged to receive the rotating shaft; a cavity portion arranged
to contain the sleeve; and a plurality of ribs provided on an inner
surface of the cavity portion and extending in the axial direction,
the ribs being spaced from each other in a circumferential
direction centered on the rotating shaft, and arranged to make
contact with at least a portion of an outer surface of the sleeve;
wherein at least one of the ribs is a varied width rib having a
circumferential width that varies with respect to the axial
direction in at least a partial section of an entire axial length
thereof.
16. The bearing structure according to claim 15, wherein the
circumferential width of an axial end of the varied width rib on an
axially opening portion side is smaller than the circumferential
width on an opposite axial end of the varied width rib.
17. The bearing structure according to claim 15, wherein the
circumferential width of the varied width rib gradually decreases
toward an axially opening portion side of the varied width rib.
18. The bearing structure according to claim 15, wherein the varied
width rib includes: a uniform width section provided on a side
opposite to an axially opening portion side, such that the width of
the varied width rib in the circumferential direction is uniform
with respect to the axial direction; and a decreased width section
provided on the axially opening portion side of the uniform width
section of the varied width rib to be adjacent to the uniform width
section such that the circumferential width of the varied width rib
is smaller than in the uniform width section.
19. The bearing structure according to claim 15, wherein the
plurality of ribs include: the varied width rib; and a uniform
width rib having a circumferential width that is uniform with
respect to the axial direction.
20. The bearing structure according to claim 15, wherein an axial
position of a center of gravity of a rotating body including the
rotating shaft either substantially coincides with, or is located
more on an axially cavity portion side than, an axial position on
the axially opening portion side of an axial end of one of the
plurality of ribs having an axial end located on the axially
opening portion side that is predominantly on the axially opening
portion side of all the plurality of ribs.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a bearing structure, a
motor, and a fan apparatus.
[0003] 2. Description of the Related Art
[0004] In known bearing structures for use in fans, motors, or the
like, a plurality of ribs extending in an axial direction are
typically provided on an inner surface of a cavity portion of a
sleeve support portion arranged to support a sleeve having a
rotating shaft inserted therein. The ribs press the sleeve, which
is press fitted within the sleeve support portion, radially inward
to retain the sleeve.
[0005] Such bearing structures have some disadvantages. For
example, when the pressing force applied by the ribs of the sleeve
support portion onto the sleeve is too small, the positioning of
the sleeve and the rotating shaft may become so insufficient that a
problem, such as sway of the rotating shaft, may occur. On the
other hand, when the pressing force applied by the ribs of the
sleeve support portion onto the sleeve is too large, the sleeve may
be excessively compressed by the pressing force from the ribs such
that the sleeve may be deformed, resulting in a failure to support
the rotating shaft stably. Moreover, in some cases, the optimum
amount of the pressing force to be applied by the ribs onto the
sleeve varies at different axial positions on the sleeve.
[0006] For instance, an axial center of gravity of a rotating body
including the rotating shaft is sometimes located in that portion
of the cavity portion of the sleeve support portion which is
located toward an opening portion, in an axial direction of the
sleeve. Therefore, more careful control of the amount of the
pressing force applied by the ribs onto the sleeve is required for
that portion of the cavity portion than for the other portions.
SUMMARY OF THE INVENTION
[0007] According to a preferred embodiment of the present
invention, there is provided a bearing structure including a
rotating shaft; a sleeve being substantially tubular and having the
rotating shaft inserted therein such that the rotating shaft is
rotatable; a sleeve support portion having a bottom and being
substantially tubular, extending in an axial direction, and
arranged to support the sleeve; and a base portion connected to an
axial end of the sleeve support portion. The sleeve support portion
preferably includes an opening portion arranged to receive the
rotating shaft; a cavity portion being continuous with the opening
portion and arranged to contain the sleeve; and a plurality of ribs
provided on an inner surface of the cavity portion and extending in
the axial direction, the ribs being spaced from each other in a
circumferential direction centered on the rotating shaft. Each of
the ribs includes a contact surface arranged to make contact with
at least a portion of an outer surface of the sleeve. The ribs are
preferably defined by a plurality of types of ribs, each type of
the ribs being different in an axial position of an axial edge of
the contact surface on an axially opening portion side.
[0008] According to another preferred embodiment of the present
invention, there is provided a bearing structure preferably
including a rotating shaft; a sleeve being substantially tubular
and having the rotating shaft inserted therein such that the
rotating shaft is rotatable; a sleeve support portion having a
bottom and being substantially tubular, extending in an axial
direction, and arranged to support the sleeve; and a base portion
connected to an axial end of the sleeve support portion. The sleeve
support portion preferably includes an opening portion arranged to
receive the rotating shaft; a cavity portion being continuous with
the opening portion and arranged to contain the sleeve; and a
plurality of ribs provided on an inner surface of the cavity
portion and extending in the axial direction, the ribs being spaced
from each other in a circumferential direction centered on the
rotating shaft, and arranged to make contact with at least a
portion of the sleeve. Each of the ribs includes an opposed surface
raised toward an outer surface of the sleeve relative to the inner
surface of the cavity portion, and opposed to the outer surface of
the sleeve. At least one of the ribs is a varied projection
dimension rib, in which a radial distance between the opposed
surface and a shaft center of the rotating shaft varies with
respect to the axial direction in at least a partial section of an
entire length thereof along the axial direction.
[0009] According to yet another preferred embodiment of the present
invention, there is provided a bearing structure including a
rotating shaft; a sleeve being substantially tubular and having the
rotating shaft inserted therein such that the rotating shaft is
rotatable; a sleeve support portion having a bottom and being
substantially tubular, extending in an axial direction, and
arranged to support the sleeve; and a base portion connected to an
axial end of the sleeve support portion. The sleeve support portion
preferably includes an opening portion arranged to receive the
rotating shaft; a cavity portion being continuous with the opening
portion and arranged to contain the sleeve; and a plurality of ribs
provided on an inner surface of the cavity portion and extending in
the axial direction, the ribs being spaced from each other in a
circumferential direction centered on the rotating shaft, and
arranged to make contact with at least a portion of an outer
surface of the sleeve. At least one of the ribs is a varied width
rib, whose width in the circumferential direction varies with
respect to the axial direction in at least a partial section of an
entire length thereof along the axial direction.
[0010] In bearing structures according to preferred embodiments of
the present invention, a plurality of ribs including the contact
surface arranged to make contact with at least a portion of the
outer surface of the sleeve are provided on the inner surface of
the cavity portion of the sleeve support portion, and the ribs are
preferably defined by a plurality of types of ribs, each type of
the ribs being different in the axial position of the axial edge of
the contact surface on the axially opening portion side. Despite
their simple structure the number of ribs that make contact with
the sleeve can be reduced to easily optimize the amount of pressing
force applied by the ribs onto the sleeve for that portion of the
sleeve which is located toward the axially opening portion side so
that an appropriate reduction in the pressing force can be achieved
to reduce deformation of the sleeve (e.g., to prevent an excessive
reduction in inside diameter of the sleeve). A greater number of
ribs are arranged to make contact with a remaining portion of the
sleeve which is located on the opposite side to the axially opening
portion side, as compared to the number of ribs arranged to make
contact with that portion of the sleeve which is located toward the
axially opening portion side. This contributes to pressing the
sleeve securely so as to ensure stable support of the sleeve, while
reducing the deformation of the sleeve caused by circumferential
variations in the pressing force applied by the ribs onto the
sleeve.
[0011] Other features, elements, steps, characteristics and
advantages of the present invention will become more apparent from
the following detailed description of preferred embodiments of the
present invention with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cross-sectional view of a fan apparatus to which
a bearing structure according to a first preferred embodiment of
the present invention is applied.
[0013] FIG. 2 is a cross-sectional view of a sleeve support portion
provided in the fan apparatus as illustrated in FIG. 1.
[0014] FIG. 3 is a plan view of the sleeve support portion as
illustrated in FIG. 2, as viewed from above in an axial
direction.
[0015] FIG. 4 is a diagram illustrating a variation of the
structure of the sleeve support portion as illustrated in FIG.
3.
[0016] FIG. 5 is a cross-sectional view of a sleeve support portion
provided in a fan apparatus to which a bearing structure according
to a second preferred embodiment of the present invention is
applied.
[0017] FIG. 6 is a diagram illustrating a variation of the
structure of the sleeve support portion as illustrated in FIG.
5.
[0018] FIGS. 7A and 7B are diagrams of a varied width rib and a
uniform width rib, respectively, which are provided on a sleeve
support portion of a fan apparatus to which a bearing structure
according to a third preferred embodiment of the present invention
is applied, as viewed radially from the direction of a rotating
shaft.
[0019] FIGS. 8A, 8B, and 8C are diagrams illustrating variations of
the varied width rib as illustrated in FIG. 7A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Preferred Embodiment
[0020] Referring to FIG. 1, a fan apparatus 1 preferably includes
an impeller 2, a motor 3, a circuit board 4, a base portion 5, a
sleeve 6, a sleeve support portion 7, a plurality of stationary
vanes 8, and an outer frame portion 9. The impeller 2 preferably
includes a plurality of rotor blades 21, a rotor blade support
portion 22, and a rotating shaft 23. The motor 3 preferably
includes an armature 31, which is a stationary motor component; and
a rotor magnet 32 and a rotor holder 33, all of which are rotating
motor components. Of these components, all components that are
arranged to rotate on the rotating shaft 23 together with the
rotating shaft 23 form portions of a rotating body 10. In other
words, the impeller 2, the rotor magnet 32, and the rotor holder 33
form parts of the rotating body 10. In the following description,
for the sake of convenience, the side where the impeller 2 is
arranged and the side where the stationary vanes 8 are arranged,
along an axial direction A of the rotating shaft 23, are assumed to
be an upper side and a lower side, respectively. However, note that
the axial direction A may not necessarily coincide with the
direction of gravity.
[0021] The rotor blade support portion 22 is preferably
substantially cup-shaped, and arranged to surround the motor 3. The
rotor blades 21, which extend radially outward, are provided on an
outer surface of the rotor blade support portion 22. The rotor
blades 21 are preferably arranged at regular intervals in a
circumferential direction. The rotor holder 33, which is preferably
made of metal and substantially cylindrical, is provided on an
inner surface of the rotor blade support portion 22. The rotor
magnet 32, which is substantially cylindrical, is fixed to an inner
circumferential surface of the rotor holder 33 by, for example,
press fitting, via an adhesive, or any other suitable attachment
method. The rotating shaft 23 is located substantially in the
center of the rotor blade support portion 22, and is provided
integrally with the rotor blades 21, the rotor blade support
portion 22, and the rotor holder 33 by injection molding, for
example. Grooves are preferably formed by knurling or the like, for
example, on an outer surface of a top portion (with respect to the
axial direction A) of the rotating shaft 23. During the injection
molding, resin flows into the grooves, so that the rotating shaft
23 and the rotor blade support portion 22 are firmly coupled with
each other.
[0022] The armature 31 of the motor 3 is supported by the base
portion 5 as described below. The armature 31 and the rotor magnet
32 are arranged radially opposite to each other. The circuit board
4, which is positioned below the armature 31 with respect to the
axial direction A, is fixed to the base portion 5, and electrically
connected to the armature 31 via conductive pins or the like, for
example. In addition, the circuit board 4 includes a circuit
designed to control current supplied to the motor 3, and is
electrically connected to an external power supply (not shown) via
a lead wire (not shown) or the like. Once the current, a control
signal, and so on are supplied to the armature 31 from the external
power supply via the lead wire or the like and the circuit board 4,
torque is produced due to electromagnetic interaction between the
armature 31 and the rotor magnet 32. This causes the rotating body
10 including the impeller 2 to rotate on a shaft center 23a of the
rotating shaft 23, allowing the rotor blades 21 to produce a flow
of air substantially in the axial direction A.
[0023] The base portion 5 has a bottom, is substantially
cylindrical, is positioned radially inward of the outer frame
portion 9, and is arranged to support the armature 31 of the motor
3 and the circuit board 4. Moreover, a lower end (with respect to
the axial direction A) of the sleeve support portion 7 is connected
to the base portion 5. The structures of the sleeve 6 and the
sleeve support portion 7 will be described in detail below.
[0024] The stationary vanes 8 are arranged upstream or downstream
of the rotor blades 21 of the impeller 2 with respect to the flow
of air generated by the rotation of the rotor blades 21, and
control the flow of air taken in or sent out by the rotor blades
21. In the present preferred embodiment, the stationary vanes 8 are
arranged below the rotor blades 21, downstream thereof, with
respect to the axial direction A. The stationary vanes 8 are
arranged at regular intervals in the circumferential direction
between the outer frame portion 9 and the base portion 5. The
stationary vanes 8 have both ends thereof joined to the outer frame
portion 9 and the base portion 5, to support the base portion 5.
The outer frame portion 9 is arranged to surround the impeller 2.
The base portion 5, the sleeve support portion 7, the stationary
vanes 8, and the outer frame portion 9 may be formed integrally by
molding using resin or metal (e.g., aluminum) to define a single
continuous member, for example. An example of a die applicable in
this molding process is a type of mold that allows the mold to
release in the axial direction A.
[0025] The sleeve 6 is preferably substantially tubular (and in the
present preferred embodiment, substantially cylindrical), and has
the rotating shaft 23 inserted therein such that the rotating shaft
is rotatable. The sleeve 6 is, for example, made of porous sintered
metal obtained by heating and consolidating metal particles, and is
impregnated with lubricating fluid such as oil. The lubricating
fluid, exuding from the sleeve 6, reduces friction between the
sleeve 6 and the rotating shaft 23.
[0026] An upper small diameter portion 6f, a lower small diameter
portion 6g, and an intermediate large diameter portion 6h are
provided on an inner surface 6d of the sleeve 6. During a process
of producing the sleeve 6, a reduced diameter portion 6e, with a
decreased outer diameter, is defined at a lower end portion (with
respect to the axial direction A) of an outer surface of the sleeve
6.
[0027] The upper small diameter portion 6f and the lower small
diameter portion 6g, which have substantially the same inside
diameter, are provided at an upper end portion and a lower end
portion (with respect to the axial direction A), respectively, of
the inner surface 6d of the sleeve 6. The intermediate large
diameter portion 6h, which has a larger inside diameter than those
of the upper and lower small diameter portions 6f and 6g, is
provided between the upper and lower small diameter portions 6f and
6g along the axial direction A. A suitable gap is secured between
the intermediate large diameter portion 6h and the rotating shaft
23. A purpose of the provision of the intermediate large diameter
portion 6h is to reduce an area of contact between the inner
surface 6d of the sleeve 6 and the rotating shaft 23, and thereby
reduce frictional resistance. An additional purpose of the
provision of the intermediate large diameter portion 6h is to
secure space to retain the lubricating fluid inside the sleeve 6.
Accordingly, in that portion of the sleeve 6 where the intermediate
large diameter portion 6h is provided, deformation of the inner
surface 6d of the sleeve 6 which might be caused by a pressing
force applied by ribs 73 and 74 would be less likely to affect the
support of the rotating shaft 23.
[0028] A method of producing the sleeve 6 will now be described
briefly below. A substantially tubular object is first formed by,
for example, powder pressing, and the upper small diameter portion
6f and the intermediate large diameter portion 6h are formed on the
inner surface 6d of the substantially tubular object. At this
stage, the lower small diameter portion 6g has not been formed yet,
and a portion corresponding to the lower small diameter portion 6g
has substantially the same inside diameter as that of the
intermediate large diameter portion 6h. At this stage, the outer
diameter of an outer surface of the substantially tubular object is
substantially the same throughout the length thereof along the
axial direction A. Then, this aggregate of solid particles obtained
by the powder pressing is heated to form a sintered body of the
above-described shape.
[0029] Next, a sizing bar having an outer diameter substantially
the same as the inside diameter of the upper small diameter portion
6f is inserted in the center of the sintered body. Further, the
sintered body is subjected to press working such that a lower end
portion (with respect to the axial direction A) of an outer surface
of the sintered body is pressed against the sizing bar. As a
result, the lower small diameter portion 6g, whose inside diameter
is substantially the same as the outer diameter of the sizing bar,
is formed at a lower end portion (with respect to the axial
direction A) on an inner surface of the sintered body. In addition,
the reduced diameter portion 6e, which is smaller in outer diameter
than an outer surface 6a of the sleeve 6, is formed at the lower
end portion (with respect to the axial direction A) of the outer
surface of the sintered body, as a result of the above-described
press working.
[0030] As illustrated in FIGS. 2 and 3, the sleeve support portion
7 extends along the axial direction A, has a bottom and is
substantially tubular and thus surrounds and supports the sleeve 6.
In more detail, the sleeve support portion 7 is provided with an
opening portion 71, a cavity portion 72, and a plurality of ribs 73
and 74.
[0031] The opening portion 71 is provided at an upper end (with
respect to the axial direction A) of the sleeve support portion 7,
and is arranged to receive the rotating shaft 23 and the sleeve 6.
Note that an additional opening portion may be provided at a lower
end (with respect to the axial direction A) of the sleeve support
portion 7. In this case, at the time of production, the sleeve 6
may be inserted through the additional opening portion at the lower
end and, for example, press fit within the sleeve support portion
7, and then the additional opening portion at the lower end may be
closed.
[0032] The cavity portion 72 is provided below the opening portion
71 with respect to the axial direction A, and is continuous with
the opening portion 71, and arranged to contain the sleeve 6. In
the present preferred embodiment, an inner surface 72a of the
cavity portion 72 is substantially in the shape of a cylinder
extending along the axial direction A.
[0033] The plurality of ribs 73 and 74 are provided on the inner
surface 72a of the sleeve support portion 7, and extend
substantially in the axial direction A. The ribs 73 and 74 are
arranged to be spaced from one another in a circumferential
direction centered on the rotating shaft 23. In addition, the ribs
73 and 74 have contact surfaces 73a and 74a which are arranged to
make contact with at least a portion of the outer surface 6a of the
sleeve 6. After the sleeve 6 is inserted through the opening
portion 71 and press fit within the cavity portion 72, the contact
surfaces 73a and 74a of the ribs 73 and 74 are in contact with the
outer surface 6a of the sleeve 6 so as to be pressed radially
inward against the outer surface 6a of the sleeve 6. This allows
the sleeve 6 to be positioned and held within the cavity portion
72. In a situation where the sleeve 6 is held within the cavity
portion 72, both ends 6b and 6c (with respect to the axial
direction A) of the sleeve 6 are located within the cavity portion
72 (see FIG. 1). In more detail, in a situation where the rotating
shaft 23 is inserted in the sleeve 6 held within the cavity portion
72, a lower end (with respect to the axial direction A) of the
rotating shaft 23 and the lower end 6c (with respect to the axial
direction A) of the sleeve 6 are located at a bottom of the cavity
portion 72, i.e., at a lower end (with respect to the axial
direction A) of the cavity portion 72.
[0034] Referring to FIG. 2, the ribs 73 and 74 as described above
have edge positions 73b and 74b at edges of the contact surfaces
73a and 74a on a side (with respect to the axial direction A) where
the opening portion 71 is provided (this side will be hereinafter
referred to simply as an "axially opening portion side" as
appropriate). The edge positions 73b and 74b have a plurality of
positions, each of the positions being different with respect to
the axial direction A. In the present preferred embodiment, there
are two types of ribs, i.e., greater-length ribs 73 and
shorter-length ribs 74. The edge position 73b of the contact
surface 73a of each of the greater-length ribs 73 is arranged
closer to the axially opening portion side than the edge position
74b of the contact surface 74a of each of the shorter-length ribs
74. Edge positions 73c and 74c of the contact surfaces 73a and 74a
of the greater-length and shorter-length ribs 73 and 74, on an
opposite side to the axially opening portion side, are at
substantially the same position with respect to the axial direction
A. In the present preferred embodiment, the edge positions 73c and
74c of the greater-length and shorter-length ribs 73 and 74 are
located at a lower end (with respect to the axial direction A) of
the cavity portion 72, on the opposite side to the axially opening
portion side. Note that, in the present preferred embodiment, the
edge positions 73c and 74c substantially coincide with positions of
ends of the ribs 73 and 74 on the opposite side to the axially
opening portion side.
[0035] The number of greater-length ribs 73 as described above is
at least one (three in the present preferred embodiment), and the
number of shorter-length ribs 74 is at least one (three in the
present preferred embodiment) (see FIG. 3). The greater-length and
shorter-length ribs 73 and 74 are arranged alternately and at
regular intervals in the circumferential direction, and arranged to
be axially symmetrical with respect to the shaft center 23a.
[0036] Referring to FIG. 2, a center of gravity Bc of the rotating
body 10 is either located at substantially the same axial position
as an end 73d or 74d, on the axially opening portion side, of the
rib 73 or 74 that is most on the axially opening portion side of
all the plurality of ribs 73 and 74, or located more on the cavity
portion 72 side with respect to the axial direction A (this side
will be hereinafter referred to as an "axially cavity portion side"
as appropriate) than that end 73d or 74d. Specifically, in the
present preferred embodiment, the center of gravity Bc of the
rotating body 10 is either located at substantially the same axial
position as the end 73d of the greater-length ribs 73 on the
axially opening portion side, or located more on the axially cavity
portion side than that end 73d. In more detail, in the present
preferred embodiment, the center of gravity Bc of the rotating body
10 is located between the edge position 73b of the contact surface
73a of the greater-length ribs 73 and the edge position 74b of the
contact surface 74a of the shorter-length ribs 74 with respect to
the axial direction A.
[0037] Moreover, in the present preferred embodiment, the end 6b of
the sleeve 6 on the axially opening portion side is located, with
respect to the axial direction A, between the edge position 73b of
the contact surface 73a of the greater-length ribs 73 and the edge
position 74b of the contact surface 74a of the shorter-length ribs
74. Note, however, that the center of gravity Bc of the rotating
body 10 is located, with respect to the axial direction A, more on
the axially cavity portion side than the end 6b of the sleeve 6 on
the axially opening portion side, but toward the axially opening
portion side.
[0038] In the present preferred embodiment, the center of gravity
Bc of the rotating body 10 is located in that portion of the sleeve
6 which is located toward the axially opening portion side.
Therefore, the amount of the pressing force applied by the
greater-length and shorter-length ribs 73 and 74 to that portion of
the sleeve 6 which is located toward the axially opening portion
side is a very important factor for stable support of the rotating
shaft 23.
[0039] In this connection, in the present preferred embodiment, the
contact surfaces 73a and 74a of the greater-length and
shorter-length ribs 73 and 74 provided on the inner surface 72a of
the cavity portion 72 of the sleeve support portion 7 have
different edge positions 73b and 74b with respect to the axial
direction A, as described above. In addition, the center of gravity
Bc of the rotating body 10 is located, with respect to the axial
direction A, between the edge position 73b of the contact surface
73a of the greater-length ribs 73 and the edge position 74b of the
contact surface 74a of the shorter-length ribs 74. Accordingly,
only the contact surfaces 73a of the greater-length ribs 73, and
not the contact surfaces 74a of the shorter-length ribs 74, make
contact with the outer surface 6a of that portion of the sleeve 6
which is located toward the axially opening portion side and where
the center of gravity Bc of the rotating body 10 is located.
[0040] Further, in the present preferred embodiment, the reduced
diameter portion 6e is provided on the outer surface of the sleeve
6, as described above. Neither the greater-length ribs 73 nor the
shorter-length ribs 74 make contact with the reduced diameter
portion 6e. That is, each of the greater-length and shorter-length
ribs 73 and 74 makes contact with only the other portions of the
outer surface 6a than the reduced diameter portion 6e, so as to
ensure a sufficient strength of the support of the sleeve 6 by the
sleeve support portion 7. Thus, the support strength increases as
the number of ribs increases. In the present preferred embodiment,
the combined total number of the greater-length and shorter-length
ribs is six, but it should be noted that any desirable number of
ribs could be provided.
[0041] Notice here that an increase in the support strength leads
to an increase in radially inward deformation of the inner surface
6d of the sleeve 6. As such, in the present preferred embodiment,
regarding that portion of the sleeve 6 which is located at an end
portion on the axially opening portion side and where the upper
small diameter portion 6f is provided on the inner surface 6d of
the sleeve 6 also, countermeasures against the radially inward
deformation can be taken, as described above, by arranging only the
contact surfaces 73a of the greater-length ribs 73, and not the
contact surfaces 74a of the shorter-length ribs 74, to make contact
with the outer surface 6a of that portion, for example.
[0042] Regarding the intermediate large diameter portion 6h, a
relatively large radial gap is secured between the rotating shaft
23 and the intermediate large diameter portion 6h. Therefore,
characteristics of the bearing mechanism will seldom be affected by
a slight radially inward deformation of the intermediate large
diameter portion 6h which may be caused by the pressure applied
radially from the outside. In the present preferred embodiment,
both the greater-length and shorter-length ribs 73 and 74 make
contact with that portion of the outer surface 6a which is located
radially outward of the intermediate large diameter portion 6h, so
as to ensure sufficient support strength thereat.
[0043] This allows an appropriate reduction in the radially inward
pressing force applied onto that portion of the sleeve 6 which is
located toward the axially opening portion side and where the
center of gravity Bc of the rotating body 10 and the upper small
diameter portion 6f of the sleeve 6 are located. Moreover, it is
made easier to optimize the amount of the pressing force applied by
the ribs 73 and 74, to reduce any deformation of the sleeve 6
(e.g., to prevent an excessive reduction in the inside diameter of
the sleeve 6). Further, both the contact surfaces 73a of the
greater-length ribs 73 and the contact surfaces 74a of the
shorter-length ribs 74 make contact with that portion of the outer
surface 6a of the sleeve 6 which is located on the axially cavity
portion side of both a portion thereof corresponding to the
position of the center of gravity Bc of the rotating body 10 and a
portion thereof corresponding to the upper small diameter portion
6f. Therefore, the number of ribs that press the sleeve 6 is
greater, by the number of shorter-length ribs 74, at that portion
of the outer surface 6a of the sleeve 6 which is located on the
axially cavity portion side of both the portion thereof
corresponding to the position of the center of gravity Bc of the
rotating body 10 and the portion thereof corresponding to the upper
small diameter portion 6f than at the portion thereof corresponding
to the upper small diameter portion 6f. This contributes to
reducing the deformation of the sleeve 6 caused by circumferential
variations in the pressing force applied by the greater-length and
shorter-length ribs 73 and 74 onto the sleeve 6, while pressing the
sleeve 6 securely to ensure the stable support of the sleeve 6.
Furthermore, the greater-length ribs 73 apply necessary pressing
force onto that portion of the sleeve 6 which is located toward the
axially opening portion side and where the center of gravity Bc of
the rotating body 10 is located, to position the sleeve 6 and
ensure the stable support of the sleeve 6.
[0044] Furthermore, the greater-length and shorter-length ribs 73
and 74 are arranged alternately in the circumferential direction.
Therefore, the pressing force applied by the greater-length ribs 73
onto that portion of the sleeve 6 which is located toward the
axially opening portion side is well balanced with respect to the
circumferential direction. Thus, the circumferential variations in
the pressing force applied by the greater-length ribs 73 onto the
sleeve 6 are reduced, so that the deformation of the sleeve 6 can
be reduced.
[0045] Furthermore, the greater-length and shorter-length ribs 73
and 74 are arranged to be axially symmetrical with respect to the
shaft center 23a. This allows the pressing force applied by the
greater-length and shorter-length ribs 73 and 74 onto the sleeve 6
to be axially symmetrical with respect to the shaft center 23a.
This allows the sleeve 6 to be stably supported by the
greater-length and shorter-length ribs 73 and 74, and contributes
to reducing the circumferential variations in the pressing force
applied by the greater-length and shorter-length ribs 73 and 74
onto the sleeve 6, to reduce the deformation of the sleeve 6.
[0046] Furthermore, in the present preferred embodiment, both ends
6b and 6c of the sleeve 6 with respect to the axial direction A are
located within the cavity portion 72 of the sleeve support portion
7. Therefore, the majority of the entire length of the sleeve 6
along the axial direction A is pressed by the greater-length and
shorter-length ribs 73 and 74 of the sleeve support portion 7, to
ensure the stable support of the sleeve 6. Moreover, in the case
where the lubricating fluid is used to reduce the friction between
the sleeve 6 and the rotating shaft 23, the lubricant is less
likely to leak out from within the cavity portion 72 of the sleeve
support portion 7.
[0047] Referring to FIG. 3, in the present preferred embodiment, a
circumferential width W1 of the greater-length ribs 73 is
substantially equal to a circumferential width W2 of the
shorter-length ribs 74. Note, however, that the circumferential
widths W1 and W2 may have different values in other preferred
embodiments of the present invention.
[0048] Also, referring to FIG. 3, in the present preferred
embodiment, a radial distance D1 between the contact surface 73a of
the greater-length rib 73 and the shaft center 23a and a radial
distance D2 between the contact surface 74a of the shorter-length
rib 74 and the shaft center 23a are set at substantially the same
value, before the sleeve 6 is, for example, press fitted within the
sleeve support portion 7. Note, however, that the radial distances
D1 and D2 may be set at different values in other preferred
embodiments of the present invention.
[0049] In the present preferred embodiment, both the number of
greater-length ribs 73 and the number of shorter-length ribs 74 are
three. Note, however, that both the number of greater-length ribs
73 and the number of shorter-length ribs 74 may be two or more than
three in other preferred embodiments of the present invention. Also
note that the number of greater-length ribs 73 and the number of
shorter-length ribs 74 may be different in other preferred
embodiments of the present invention.
[0050] In the present preferred embodiment, two types of ribs,
i.e., the greater-length ribs 73 and the shorter-length ribs 74,
are provided. Note, however, that in other preferred embodiments of
the present invention, three or more types of ribs may be provided,
each type of ribs being different in the edge position of the
contact surface on the axially opening portion side with respect to
the axial direction A. In a preferred embodiment as illustrated in
FIG. 4, for example, three types of ribs 75, 76, and 77, with three
ribs for each type, are arranged at regular intervals in the
circumferential direction so as to be axially symmetrical with
respect to the shaft center 23a. As to the edge position of the
contact surface on the axially opening portion side in the three
types of ribs, the edge position of the ribs 75 is located most on
the axially opening portion side, the edge position of the ribs 77
is located most on the axially cavity portion side, and the edge
position of the ribs 76 is located at an intermediate position
between them.
Second Preferred Embodiment
[0051] FIG. 5 is a cross-sectional view of a sleeve support portion
7 provided in a fan apparatus 1 to which a bearing structure
according to a second preferred embodiment of the present invention
is applied. The fan apparatus 1 according to the present preferred
embodiment is essentially identical to the fan apparatus 1
according to the first preferred embodiment except in the structure
of ribs 171 and 172. Accordingly, like portions are designated by
like reference numerals and redundant description is omitted.
[0052] Referring to FIG. 5, in the present preferred embodiment, at
least one of the ribs 171 and 172 provided on the inner surface 72a
of the sleeve support portion 7 is not uniform in the radial
dimension, i.e., in how far it projects from the inner surface 72a
of the sleeve support portion 7 toward the shaft center 23a. This
type of ribs will be referred to as "varied projection dimension
ribs" as appropriate. In at least a partial section of the axial
length (along the axial direction A) of each varied projection
dimension rib 171, a radial distance D3 between the shaft center
23a and an opposed surface 171a of the varied projection dimension
rib 171, which is opposed to the outer surface 6a of the sleeve 6,
varies with respect to the axial direction A.
[0053] In the present preferred embodiment, at least one varied
projection dimension rib 171 and at least one uniform projection
dimension rib 172 are provided on the inner surface 72a of the
sleeve support portion 7. As to the uniform projection dimension
rib 172, a radial distance D4 between the shaft center 23a and an
opposed surface 172a of the uniform projection dimension rib 172,
which is opposed to the outer surface 6a of the sleeve 6, is
substantially uniform along an entire length of the uniform
projection dimension rib 172 along the axial direction A. More
specifically, in the present preferred embodiment, a plurality of
(e.g., three) varied projection dimension ribs 171 and a plurality
of (e.g., three) uniform projection dimension ribs 172 are arranged
at regular intervals in the circumferential direction to be axially
symmetrical with respect to the shaft center 23a. In a variation of
the present preferred embodiment, all the ribs provided on the
inner surface 72a of the sleeve support portion 7 may be composed
of varied projection dimension ribs 171. Both ends 171b and 171c
(with respect to the axial direction A) of the varied projection
dimension rib 171 are located at substantially the same axial
positions as both ends 172b and 172c, respectively, of the uniform
projection dimension rib 172. In more detail, in the present
preferred embodiment, the end 171c of the varied projection
dimension rib 171 on the axially cavity portion side (i.e., on the
lower side with respect to the axial direction A) and the end 172c
of the uniform projection dimension rib 172 on the axially cavity
portion side (i.e., on the lower side with respect to the axial
direction A) are located at the end of the cavity portion 72 on the
axially cavity portion side (i.e., on the lower side with respect
to the axial direction A).
[0054] In addition, in the present preferred embodiment, an
enlarging section 171d is provided at an end portion of the varied
projection dimension rib 171 on the axially opening portion side.
In the enlarging section 171d, the distance D3 between the opposed
surface 171a and the shaft center 23a gradually increases toward
the axially opening portion side. A uniform section 171e, where the
distance D3 is uniform with respect to the axial direction A, is
provided at that portion of the varied projection dimension rib 171
which is located on the axially cavity portion side of the
enlarging section 171d in the opposed surface 171a. In a variation
of the present preferred embodiment, the enlarging section 171d may
extend over substantially the entire length of the opposed surface
171a of the varied projection dimension rib 171 along the axial
direction A.
[0055] As such, the sleeve 6 has a portion with which the enlarging
section 171d of the opposed surface 171a of the varied projection
dimension rib 171 makes contact. In this portion of the sleeve 6
opposite to the enlarging section 171d, the amount of the pressing
force applied by the opposed surface 171a of the varied projection
dimension rib 171 decreases toward the axially opening portion
side.
[0056] Also in the present preferred embodiment, the center of
gravity Bc of the rotating body 10 is located in that portion of
the sleeve 6 which is located toward the axially opening portion
side with respect to the axial direction A. In addition, the center
of gravity Bc of the rotating body 10 is either located at
substantially the same axial position as the ends 171b and 172b of
the varied and uniform projection dimension ribs 171 and 172 on the
axially opening portion side, or located more on the axially cavity
portion side than the ends 171b and 172b. Therefore, the enlarging
section 171d of the opposed surface 171a of the varied projection
dimension rib 171 substantially corresponds to that portion of the
outer surface 6a of the sleeve 6 where the center of gravity Bc of
the rotating body 10 is located.
[0057] In addition, in the present preferred embodiment, it is
possible to allow the enlarging section 171d of the opposed surface
171a of the varied projection dimension rib 171 to correspond to an
end portion of the outer surface 6a of the sleeve 6 on the axially
opening portion side where the upper small diameter portion 6f is
provided on the inner surface 6d of the sleeve 6.
[0058] This allows an appropriate reduction in the radially inward
pressing force applied onto that portion of the sleeve 6 which is
located toward the axially opening portion side and where the
center of gravity Bc of the rotating body 10 and the upper small
diameter portion 6f of the sleeve 6 are located. Moreover, it is
made easier to optimize the amount of the pressing force applied by
the ribs 171 and 172, to reduce the deformation of the sleeve 6
(e.g., to prevent an excessive reduction in the inside diameter of
the sleeve 6). In addition, the uniform section 171e of the opposed
surface 171a of the varied projection dimension rib 171 and the
opposed surface 172a of the uniform projection dimension rib 172
are arranged to make contact with that portion of the outer surface
6a of the sleeve 6 which is located on the axially cavity portion
side of that portion of the sleeve 6 where the center of gravity Bc
of the rotating body 10 is located. This leads to an increase in
the number of ribs 171 and 172 pressing the sleeve 6, or in the
area of contact. This contributes to reducing the deformation of
the sleeve 6 caused by circumferential variations in the pressing
force applied by the ribs 171 and 172 onto the sleeve 6, while
allowing the ribs 171 and 172 to press the sleeve 6 securely to
ensure the stable support of the sleeve 6. That is, it is possible
to secure a sufficient total number of varied and uniform
projection dimension ribs 171 and 172 to effectively reduce the
deformation of the sleeve 6 caused by the circumferential
variations in the pressing force applied by the ribs 171 and 172.
In addition, the use of the varied and uniform projection dimension
ribs 171 and 172 contributes to partially reducing the pressing
force applied onto that portion of the sleeve 6 which is located
toward the axially opening portion side and which is concerned with
problems such as the problem of the excessive reduction in the
inside diameter of the sleeve 6 caused by the pressing force
applied by the ribs 171 and 172.
[0059] Moreover, the combined use of the varied and uniform
projection dimension ribs 171 and 172 produces a beneficial effect
as described below. The uniform projection dimension rib 172, in
which the radial distance D4 between the opposed surface 172a and
the shaft center 23a is uniform with respect to the axial direction
A, applies the pressing force to the sleeve 6 substantially
uniformly with respect to the axial direction A. Therefore, the
uniform projection dimension rib 172 supports each axial position
of the sleeve 6 stably. In addition, the additional use of the
varied projection dimension rib 171 allows optimization of the
amount of the pressing force applied by the varied and uniform
projection dimension ribs 171 and 172 to each axial position of the
sleeve 6.
[0060] Furthermore, the varied and uniform projection dimension
ribs 171 and 172 are arranged alternately in the circumferential
direction. This contributes to preventing the addition of the
varied projection dimension ribs 171 from causing uneven
circumferential distribution of the pressing force applied by the
varied and uniform projection dimension ribs 171 and 172 onto the
sleeve 6 (this is especially true for that portion of the sleeve 6
which is located toward the axially opening portion side). This
contributes to achieving the stable support of the sleeve 6, while
reducing the deformation of the sleeve 6 caused by the
circumferential variations in the pressing force applied by the
ribs 171 and 172 onto the sleeve 6.
[0061] Furthermore, the varied and uniform projection dimension
ribs 171 and 172 are arranged to be axially symmetrical with
respect to the shaft center 23a. This allows the pressing force
applied by the varied and uniform projection dimension ribs 171 and
172 onto the sleeve 6 to be axially symmetrical with respect to the
shaft center 23a. This allows the sleeve 6 to be stably supported
by the varied and uniform projection dimension ribs 171 and 172,
and contributes to reducing the circumferential variations in the
pressing force applied by the ribs 171 and 172 onto the sleeve 6,
to reduce the deformation of the sleeve 6.
[0062] Referring to FIG. 6, in still another variation of the
present preferred embodiment, regarding the varied projection
dimension rib 171, an end 171f, on the axially opening portion
side, of the enlarging section 171d of the opposed surface 171a of
the varied projection dimension rib 171 and a boundary portion 171g
between the enlarging section 171d and the uniform section 171e may
be in the shape of a smooth curve in a section taken along the
axial direction A. Note that, in addition to the shape as
illustrated in FIG. 6, the opposed surface 171a of the varied
projection dimension rib 171 may be in various other shapes in
section taken along the axial direction A, in other preferred
embodiments of the present invention.
Third Preferred Embodiment
[0063] FIGS. 7A and 7B are diagrams of a varied width rib 271 and a
uniform width rib 272, respectively, which are provided on a sleeve
support portion 7 of a fan apparatus 1 to which a bearing structure
according to a third preferred embodiment of the present invention
is applied, as viewed radially from the direction of the rotating
shaft 23. The fan apparatus 1 according to the present preferred
embodiment is essentially identical to the fan apparatus 1
according to the first preferred embodiment except in the structure
of the varied and uniform width ribs 271 and 272. Accordingly, like
portions are designated by like reference numerals, and redundant
description is omitted.
[0064] In the present preferred embodiment, as illustrated in FIGS.
7A and 7B, at least one of the ribs 271 and 272 provided on the
inner surface 72a of the sleeve support portion 7 is not uniform in
width. This type of ribs will be referred to as "varied width ribs"
as appropriate. In at least a partial section of the axial length
of each varied width rib 271, a width W3 in a circumferential
direction C centered on the shaft center 23a varies with respect to
the axial direction A.
[0065] In the present preferred embodiment, at least one varied
width rib 271 and at least one uniform width rib 272 are provided
on the inner surface 72a of the sleeve support portion 7. As to the
uniform width rib 272, a width W4 in the circumferential direction
C is substantially uniform over its entire axial length. More
specifically, in the present preferred embodiment, a plurality of
(e.g., three) varied width ribs 271 and a plurality of (e.g.,
three) uniform width ribs 272 are arranged at regular intervals in
the circumferential direction to be axially symmetrical with
respect to the shaft center 23a. In a variation of the present
preferred embodiment, all the ribs provided on the inner surface
72a of the sleeve support portion 7 may be varied width ribs 271.
Both ends 271b and 271c (with respect to the axial direction A) of
the varied width rib 271 are located at substantially the same
axial positions as both ends 272b and 272c, respectively, of the
uniform width rib 272. In more detail, in the present preferred
embodiment, the end 271c of the varied width rib 271 on the axially
cavity portion side (i.e., on the lower side with respect to the
axial direction A) and the end 272c of the uniform width rib 272 on
the axially cavity portion side (i.e., on the lower side with
respect to the axial direction A) are located at the end of the
sleeve support portion 7 on the axially cavity portion side (i.e.,
on the lower side with respect to the axial direction A).
[0066] Also, in the present preferred embodiment, a decreased width
section 271d is provided at an end portion of the varied width rib
271 on the axially opening portion side, while a uniform width
section 271e is provided to extend from an end of the decreased
width section 271d on the axially cavity portion side to the end of
the varied width rib 271 on the axially cavity portion side. In the
decreased width section 271d, the width W3 of the varied width rib
271 is smaller than the width W3 of the varied width rib 271 in the
uniform width section 271e, and the width W3 gradually decreases
toward the axially opening portion side. In the uniform width
section 271e, the width W3 of the varied width rib 271 is uniform
with respect to the axial direction A.
[0067] Here, referring to FIG. 7A, both side surfaces 271f and
271g, in the circumferential direction C, of the varied width rib
271 in the decreased width section 271d may assume a tapered shape
such that the width W3 decreases substantially linearly toward the
axially opening portion side. Alternatively, referring to FIG. 8A,
the side surfaces 271f and 271g may assume a curved shape such that
the width W3 decreases at an increasing rate toward the axially
opening portion side. Referring to FIG. 8B, in another variation of
the present preferred embodiment, the width W3 of the varied width
rib 271 in the decreased width section 271d may be uniform with
respect to the axial direction A (but is smaller than the width W3
in the uniform width section 271e). Referring to FIG. 8C, in still
another variation of the present preferred embodiment, the width W3
may gradually decrease toward the axially opening portion side over
the entire axial length of the varied width rib 271. Referring to
FIG. 8C, note that both side surfaces, in the circumferential
direction, of the varied width rib 271 may be laterally
asymmetrical when viewed radially from the inside.
[0068] As described above, the width W3 of the varied width rib 271
is smaller in the decreased width section 271d than in the uniform
width section 271e. Accordingly, the amount of the pressing force
applied by a contact surface 271a of the varied width rib 271 is
smaller for that portion of the sleeve 6 which makes contact with
the decreased width section 271d of the varied width rib 271 than
for that portion of the sleeve 6 which makes contact with the
uniform width section 271e. In particular, according to the
structures as illustrated in FIGS. 7A and 8A, the width W3 of the
varied width rib 271 in the decreased width section 271d gradually
decreases toward the axially opening portion side; therefore, the
amount of the pressing force applied by the varied width rib 271
becomes progressively smaller toward the axially opening portion
side, for that portion of the sleeve 6 which makes contact with the
decreased width section 271d of the varied width rib 271. As to the
uniform width rib 272, the width W4 is substantially uniform over
its entire axial length, and accordingly, the amount of the
pressing force applied by the uniform width rib 272 onto the sleeve
6 is substantially uniform with respect to the axial direction
A.
[0069] In the present preferred embodiment also, the center of
gravity Bc of the rotating body 10 is, with respect to the axial
direction A, located in that portion of the sleeve 6 which is
located toward the axially opening portion side. In addition, the
center of gravity Bc of the rotating body 10 is either located at
substantially the same axial position as the ends 271b and 272b of
the varied and uniform width ribs 271 and 272 on the axially
opening portion side, or located more on the axially cavity portion
side than the ends 271b and 272b. In particular, according to the
structures as illustrated in FIGS. 7A, 8A, and 8B, the decreased
width section 271d of the varied width rib 271 substantially
corresponds to that portion of the outer surface 6a of the sleeve 6
where the center of gravity Bc of the rotating body 10 is
located.
[0070] In addition, in the present preferred embodiment, it is
possible to allow the decreased width section 271d of the varied
width rib 271 to correspond to an end portion of the outer surface
6a of the sleeve 6 on the axially opening portion side where the
upper small diameter portion 6f is provided on the inner surface 6d
of the sleeve 6.
[0071] Therefore, the addition of the varied width rib 271 as
described above allows an appropriate reduction in the radially
inward pressing force applied onto that portion of the sleeve 6
which is located toward the axially opening portion side and where
the center of gravity Bc of the rotating body 10 and the upper
small diameter portion 6f of the sleeve 6 are located, and
facilitates the optimization of the amount of the pressing force
applied by the ribs 271 and 272 so as to reduce the deformation of
the sleeve 6 (e.g., to prevent an excessive reduction in the inside
diameter of the sleeve 6). That is, the total number of varied and
uniform width ribs 271 and 272 can be set at a number that allows
an effective reduction in the deformation of the sleeve 6 caused by
circumferential variations in the pressing force applied by the
ribs 271 and 272. In addition, it is possible to partially reduce
the pressing force applied by the ribs 271 and 272 onto that
portion of the sleeve 6 which is located toward the axially opening
portion side and which is concerned with problems such as the
problem of the excessive reduction in the inside diameter of the
sleeve 6 caused by the pressing force applied by the ribs 271 and
272.
[0072] In this connection, according to the structures as
illustrated in FIGS. 7A, 8A, and 8B, the decreased width section
271d of the varied width rib 271 is arranged to substantially
correspond to the outer surface 6a of that portion of the sleeve 6
where the center of gravity Bc of the rotating body 10 and the
upper small diameter portion 6f of the sleeve 6 are located. This
allows more effective control of the pressing force applied to that
portion of the sleeve 6. Meanwhile, the uniform width section 271e
of the varied width rib 271 applies the pressing force
substantially uniformly over the axial length of that portion of
the sleeve 6 which makes contact with the uniform width section
271e of the varied width rib 271, to achieve the stable support of
the sleeve 6.
[0073] Moreover, the combined use of the varied and uniform width
ribs 271 and 272 produces a beneficial effect as described below.
The uniform width rib 272, whose width W3 is uniform with respect
to the axial direction A, applies the pressing force to the sleeve
6 substantially uniformly with respect to the axial direction A.
Therefore, the uniform width rib 272 supports each axial position
of the sleeve 6 stably. At the same time, the additional use of the
varied width rib 271 allows the optimization of the amount of the
pressing force applied by the varied and uniform width ribs 271 and
272 to each axial position of the sleeve 6.
[0074] Furthermore, the varied and uniform width ribs 271 and 272
are arranged alternately in the circumferential direction. This
contributes to preventing the addition of the varied width ribs 271
from causing uneven circumferential distribution of the pressing
force applied by the varied and uniform width ribs 271 and 272 onto
the sleeve 6 (this is especially true for that portion of the
sleeve 6 which is located toward the axially opening portion side).
This contributes to achieving the stable support of the sleeve 6,
while reducing the deformation of the sleeve 6 caused by the
circumferential variations in the pressing force applied by the
ribs 271 and 272 onto the sleeve 6.
[0075] Furthermore, the varied and uniform width ribs 271 and 272
are preferably arranged to be substantially axially symmetrical
with respect to the shaft center 23a. This allows the pressing
force applied by the varied and uniform width ribs 271 and 272 onto
the sleeve 6 to be substantially axially symmetrical with respect
to the shaft center 23a. This allows the sleeve 6 to be stably
supported by the varied and uniform width ribs 271 and 272, and
contributes to reducing the circumferential variations in the
pressing force applied by the ribs 271 and 272 onto the sleeve 6,
to reduce the deformation of the sleeve 6.
[0076] In the foregoing description of the preferred embodiments,
it has been assumed that the bearing structures according to the
preferred embodiments are applied to the fan apparatus 1. Note,
however, that the bearing structures according to the preferred
embodiments are applicable not only to the fan apparatus 1 but also
to various other devices having a bearing structure. Examples of
other applications include, for example, disc drive apparatuses
designed to rotate a disc-shaped recording medium and any other
devices that include electric motors.
[0077] While preferred embodiments of the present invention have
been described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing the scope and spirit of the present invention. The scope
of the present invention, therefore, is to be determined solely by
the following claims.
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